Tuner input filter with electronically adjustable response for adapting to antenna characteristic

ABSTRACT

A system, apparatus and/or method provides frequency response adjustment of an RF input filter of an RF tuner based on impedance of an antenna system that is providing reception of RF signals to the RF tuner. The frequency response adjustment is preferably accomplished dynamically and/or with respect to each frequency tuned. Particularly, the system, method and/or apparatus provides compensation at the RF tuner level for mistuning effects produced on the RF tuner by antenna system impedance presented at the antenna input that is other than a designed for impedance. Frequency response of an RF input filter for the RF tuner is electronically adjustable with an independent or semi-independent control voltage signal based on one or more measured parameters of a tuning frequency. Frequency response adjustment may include adjustment of a center frequency of the RF input filter bandpass frequency range and/or altering the bandpass frequency range of the RF input filter. The subject invention expands the capability of an RF signal receiver, particularly one using at least one electronically adjustable RF filter at the input of an electronic alignment type tuner.

This application is a divisional of U.S. application Ser. No.10/512,525, filed Oct. 26, 2004 now U.S. Pat. No. 7,668,519, hereinincorporated by reference.

This U.S. non-provisional patent application claims the benefit ofand/or priority to the following three U.S. provisional patentapplications, all filed on Apr. 26, 2002 and all commonly assigned: U.S.provisional patent application Ser. No. 60/376,099 entitled Tuner InputFilter With Electronically Adjustable Center Frequency For Adapting toAntenna Characteristic, U.S. provisional patent application Ser. No.60/376,127 entitled Tuner RF Input Filter With Integrated Signal BoostProvision, and U.S. provisional patent application Ser. No. 60/376,128entitled Tuner Input Filter With Electronically Adjustable Response ForAdapting to Antenna Characteristic.

CROSS REFERENCE TO RELATED APPLICATIONS

Cross reference is made to related U.S. patent application Ser. No.10/512,675 entitled Tuner Input Filter With Electronically AdjustableCenter Frequency For Adapting To Antenna Characteristic by MichaelAnthony Pugel, Gary Dean Grubbs, Edward Allen Hall, and Max WardMuterspaugh, filed on even date herewith.

BACKGROUND

1. Field of the Invention

The present invention relates to tuners for radio frequency signalreceivers such as televisions and, more particularly, to a radiofrequency tuner with an input filter having electrically adjustablefrequency characteristics base on antenna input characteristics.

2. Background Information

Most, if not all, radio frequency (RF) signal receivers, such as radios,televisions, television signal receivers, and the like, include a tunerfor selecting a particular radio frequency from the spectrum ofavailable radio frequencies that are input to the RF signal receiver.The RF signal is supplied to the receiver by an antenna and/or cabling.

Tuner RF input circuits for RF signal receivers, particularly televisionsignal receivers, are typically designed based on a known, good 75 ohmssource such as provided by cable television systems in order to providea proper expected performance. Many types of television antennas,particularly those of the indoor variety such as what are known as“rabbit ears”, are not capable of providing a good 75 ohm source. Assuch, a television antenna (and associated cabling) may present thetuner with an input impedance that is other than 75 ohms, changesthrough the frequency band of interest; and which contains a resistivecomponent and a reactive component.

The reactive portion of the input impedance will be absorbed by thesection of the RF input circuit of the tuner. The resistive componentwill, in most cases, cause the input transforming network at the RFfilter input to create the incorrect bandwidth base on the loaded Q ofthe network. The unknown impedance may cause the RF input circuit'scenter frequency to shift, resulting in a mistuning of the centerfrequency of the filter. Moreover, the effect of the antenna andassociated cabling on the RF tuner input may be to adjust the bandwidthof the RF input circuit due to incorrect resistance in the tunedcircuit. Additionally, different input circuits may exhibit an alternateeffect, whereas the input reactance causes a change in bandwidth, centerfrequency, or a combination of both may be present. The result in tunerperformance will be lower gain, higher noise figure, poor frequencyresponse, and poor adjacent channel performance. The unknown impedancemay also cause other tuning problems.

In RF signal receivers such as televisions, it is known to provide atuner employing electronic alignment. These tuners use an alignmentsystem that allows for an adjustment range on the RF tuning voltagecentered around an oscillator control voltage. Basically, these tunersuse voltage controlled RF filters for providing adjustability. When anantenna and cabling are used with respect to such electronic alignmenttuners, the effect thereof may be to adjust the tuning of the filter(s)off the desired center frequency and/or bandpass frequencycharacteristics thereof. This “mistuning” can be seen in varying degreesand in varying modes across the entire input frequency range, andadditionally varies in response to the antenna, cable, and type of inputfilter circuit employed.

It is evident from the above that what is needed is a manner ofadjusting for an unknown impedance at the input of an RF tuner of an RFsignal receiver.

It is further evident from the above that what is needed is a manner ofadjustment of frequency response of an input of an RF tuner of an RFsignal receiver based on impedance presented by an RF antenna systemthrough its effects on RF signal reception.

It is yet further evident from the above that what is needed is a mannerof dynamic adjustment of frequency response of an input of an RF tunerof an RF signal receiver based on impedance presented by an RF antennasystem through its effects on RF signal reception.

SUMMARY

A system, apparatus and/or method provides dynamic frequency responsemodification and/or adjustment of an RF input filter of an RF tuner withrespect to a received RF signal based on impedance of an RF signalreceiving antenna.

In one form, there is provided a method for tuning a signal channelcomprising the steps of: (a) selecting a signal channel to be tuned; (b)tuning the selected signal channel by applying a control signal to anelectronically tunable input filter of the signal tuner, the controlsignal causing a center frequency of the electronically tunable inputfilter to correspond to an expected frequency of the signal channel tobe tuned; (c) providing an initial control signal to the electronicallyadjustable filter corresponding to the signal channel to be tuned; (d)measuring a parameter of the tuned signal channel; (e) determining if afrequency response adjustment to the filter is necessary based on themeasured parameter; and (f) adjusting the control signal to theelectronically adjustable input filter if it is determined that anadjustment is necessary. The frequency response change may be of theform of an adjustment to the center frequency of the filter and/or anadjustment to the filter bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a simplified block diagram of an RF signal receiver embodiedas a television signal receiver having an exemplary RF tuning systemincorporating an electronically adjustable RF input filter in accordancewith the principles of the subject invention;

FIG. 2 is a block diagram of an exemplary RF signal receiver embodied asa television signal receiver having a tuning system incorporating an RFinput filter wherein frequency response thereof is electronicallyadjustable in response to input impedance produced as a result of anantenna or antenna system in accordance with the principles of thesubject invention;

FIG. 3 is a block diagram of an exemplary tuner employing electronicalignment in which the subject invention may be used;

FIG. 4 is a flowchart of an exemplary manner of adjusting the frequencyresponse of the subject RF input filter in response to the presence ofimpedance at an RF signal input to the RF input filter in accordancewith the principles of the subject invention;

FIG. 5 is a circuit diagram of an exemplary electronically adjustable RFinput filter in accordance with one aspect of the subject invention;

FIG. 6 is a circuit diagram of another exemplary electronicallyadjustable RF input filter in accordance with one aspect of the subjectinvention

FIG. 7 is a circuit diagram of the exemplary electronically adjustableRF input filter of FIG. 5 incorporating a boost control voltage scalingcircuit in accordance with an aspect of the subject invention;

FIG. 8 is a circuit diagram of the exemplary electronically adjustableRF input filter of FIG. 6 incorporating a boost control voltage scalingcircuit in accordance with an aspect of the subject invention; and

FIG. 9 is a flowchart of another exemplary manner of adjusting thefrequency response of the subject RF input filter in response to thepresence of impedance at an RF signal input to the RF input filter inaccordance with the principles of the subject invention.

Corresponding reference characters tend to indicate corresponding partsthroughout the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIG. 1, there is depicted a block diagram of an RFsignal receiver 20 to which the subject invention pertains. The RFsignal receiver 20 is preferably, but not necessarily, of the type thataccepts connection to an antenna of an unknown impedance by the user forRF signal reception rather than utilizing a fixed, known impedanceantenna. The RF signal receiver 20 may be, and thus is representativeof, any type of RF signal receiver such as a television, radio, VCR,television signal receiver, cellular phone, wireless local area network,or the like, to which a user may attach an antenna and typically anexternal antenna for receiving the RF signals. In the followingdescription of an exemplary embodiment of the invention, a televisionreceiver is described as a representative example of a system suitablefor incorporating principles of the invention. However, the principlesdiscussed herein in the context of a television receiver apply to anyform of RF signal receiver. More specifically, in the followingdescription of the subject invention, an RF signal receiver will bedescribed as a television or television signal receiver (TSR) thatreceives television signals typically in the form of television channels(i.e. television signals of different frequencies). It should beappreciated, however, that the subject invention may be utilized withall types of RF signal receivers including, but not limited to, thetypes of signal receivers identified above that select various types ofsignal channels including, but not limited to, television channels,radio channels, wireless network connection channels, cellular phonechannels, etc.

The television 20 includes a first signal input 30 that is operative,adapted and/or configured to be connected to an antenna system 24. Theantenna system 24 includes an antenna 26 and associated cabling 28. Thecabling 28 is attached to the antenna 26 and to the antenna input 30 forproviding the television signals 21 received by the antenna 26 to thetelevision 20. The antenna 22 may be of any type that is adapted,configured and/or operative to receive television signals and may be anindoor or an outdoor antenna. An example of an indoor antenna may bewhat is known as a “rabbit ears” type antenna. In all cases, the antennasystem 24 receives television signals 21 that are transmitted orbroadcast over the air. Moreover, the antenna 26 may be for analogand/or digital television signals. The antenna system 24 provides anunknown impedance Z (represented by the box 29) consisting of unknownresistive and/or reactive components. The impedance 29 is thus presentedto the antenna input 30. This impedance from the antenna is likely avariation from the nominal 75 ohms and likely will be different in somerespect for every channel received by the tuner.

The television 20 also includes a second signal input 38 that isoperative, adapted and/or configured to be connected to a cabletelevision (CATV) system 32. The CATV system 32 includes a CATV provideror headend 34 providing a plurality of television signals and cabling36. The cabling 36 connects the CATV 34 to the second input 38. The CATVsystem 32 provides a known or nominal impedance, typically 75 ohms. Inaccordance with the principles of the subject invention, the tuningsystem 22, and particularly the RF tuner 40, is designed based on theknown, good 75 ohm source provided by the CATV system 32 and cablingtherefore. It should be appreciated that the television 20 may have moretelevision signal inputs.

The first (antenna) input 30 and the second (CATV) input 38 areconnected to an input selector 48. The input selector 48, typicallyknown as an RF switch, is operative, adapted and/or configured to selecteither the antenna input 30 or the CATV input 38 (or any othertelevision signal input the television may have). The television 20 willthen provide the television channels of the selected input.Alternatively, another embodiment may not include this input selector,but rather allow only one connection of either a cable or an antenna,The tuner is reprogrammed accordingly through user controls depending onwhether an antenna is connected or a cable is connected to this commoninput.

If the antenna input 30 is selected, the input impedance 29 is thuspresented to the television and more particularly to a tuning system 22of the television. As indicated herein, such impedance varies fromnominal values and thus changes the frequency response of the tuningsystem 22, thereby changing its tuning performance.

The RF signal receiver 20 includes an RF signal tuning system (tuningsystem), generally designated 22, that is operative, adapted and/orconfigured to receive a plurality of television (TV) signals of varyingfrequencies and select or tune a particular TV frequency or channeltherefrom. The tuning system 22 includes a tuner 40 that is operative,configured and/or adapted to tune to a particular television channel inresponse to selection of a particular television channel typically viauser input. To this end, the television signal receiver 20 includeschannel selection circuitry/logic 44 that is operative, adapted and/orconfigured to receive a channel selection request and provide therequisite signals to the tuner 40 in order for the tuner 40 to tune tothe selected channel.

The tuning system 22 further includes signal processing circuitry/logic46 that receives the tuned television signal from the tuner 40. Thesignal processing circuitry/logic 46 provides signal processing for thetuned television signal as is known in the art in order to eventuallydisplay the video portion of the television channel and reproduce theaudio portion thereof. Moreover, in accordance with the principles ofthe subject invention and as described further below, the signalprocessing circuitry/logic 46 provides control signals to tuning controlcircuitry/logic 42 of the tuning system 22. The tuning controlcircuitry/logic 42 provides a voltage signal or voltage signals to atunable component or components of the tuner 40 in order to adjust thefrequency response thereof in accordance with the principles of thesubject invention.

Particularly, the tuning system 22 is operative, adapted and/orconfigured to provide frequency response adjustment of the tuner 40based on the impedance 29 of the antenna system 24. Such frequencyresponse adjustment is preferably accomplished dynamically and/or withrespect to each frequency (channel) tuned. Particularly, compensation isprovided at the tuner 40 for mistuning effects produced on the tuner 40by the antenna system 24 impedance 29 presented at the antenna input 30.Frequency response of the tuner 40 is electronically adjustable with anindependent or semi-independent control voltage signal based on one ormore measured parameters of a channel being tuned. Frequency responseadjustment may include adjustment of a center frequency, bandpassfrequency range and/or altering the bandpass frequency range of thetuner.

Referring now to FIG. 2, there is depicted a more detailed block diagramof the exemplary television signal receiver (television) 20 or ofanother television signal receiver in accordance with the principles ofthe subject invention. The television 20 of FIG. 2 performs insubstantially the same manner as described in conjunction with theembodiment of FIG. 1. The embodiment of FIG. 2, however, providesanother manner of implementing the subject invention.

In this embodiment, the tuner 40 is preferably, but not necessarily, atuner of the type employing electronic alignment. The tuner 40 includesa tunable filter such as an electronically tunable or adjustable filter16 that utilizes a control signal such as a control voltage signal inorder to change the filter or filtering characteristics thereof (i.e.the frequency response thereof such as a range of passband signals orbandpass frequency range and/or a center frequency of the passbandfrequency range). The tunable filter of the tuner 40 is an input filter,i.e. it is situated at the input of the tuner 40. The tunable filterreceives the control voltage from a control voltage generator 58 thatmay be a digital to analog converter (DAC). The tunable filter of thetuner 40 is tunable in its passband frequency range (bandpass frequencyrange) depending on the input impedance 29. Particularly, the frequencyresponse of the input filter of the tuner 40 is adjustable in responseto the impedance 29. Thus, the passband frequency range and/or a centerfrequency of the tunable filter may be adjusted. In accordance with theprinciples of the subject invention, the passband frequency range and/orthe center frequency of the tunable filter is with respect to atelevision channel. In one form, the passband frequency range and/orcenter channel is dynamically adjusted for each television channel (i.e.accomplished each time a television channel is tuned).

The television 20 includes a processor 50 that provides processing forand/or operation of the various components of the television. Theprocessor 50 executes program instructions 52 in order to provide thefunctionality and/or features described herein. The television 20 mayalso include memory 54 such as is known in the art for storing values,preferences, and/or the like. The processor 50 provides control to thechannel selection circuitry/logic 44, the signal processingcircuitry/logic 46, as well as the control voltage generator 58. Thecontrol voltage generator 58 supplies the necessary control voltages tothe tuner 40, including the tunable filter thereof for operation inaccordance with the present principles. In an exemplary embodiment ofthe above, the tuning process is for a user to select a channel. Thechannel information is then sent to a phase lock loop (PLL) forsynthesis of a correct or proper LO, which then generates a tuningvoltage which can be used for the RF filters, either directly orindirectly. Then the RF voltages for the filters can be created eitherdirectly, indirectly, or independently of the PLL LO tuning voltage.

The determination of whether to initiate adjusting the input filter ofthe tuner 40 is accomplished, in part, by measurement circuitry/logic56. The measurement circuitry/logic 56 receives a tuned channel from thetuner 40 and performs a signal measurement or signal measurementsthereon, the type of which is determined by whether the televisionsignal is an analog signal or a digital signal. While other metrics maybe used, an automatic gain control (AGC) signal may be used for ananalog signal, while AGC and/or signal quality may be used for a digitalsignal.

Referring now to FIG. 3, there is depicted a block diagram of anexemplary tuner 40 employing electronic alignment incorporating atunable input filter in accordance with the principles of the subjectinvention. The tuner 40 is operative to receive several bands of RFtelevision signals such as VHF (more particularly, two VHF band, band 1and band 2) and UHF television signals and, according to a selectedtelevision channel, provide an IF (intermediate frequency) televisionchannel signal.

The RF signals are received from the input selector 48 that providestelevision signals (channels) from either the cable system 34 or theantenna system 24. The received television channels are received by aU/V (UHF/VHF) splitter 202 that is operative to separate the UHF bandfrom the VHF bands. The U/V splitter 202 receives a control signal BSV(band select VHF) when the selected channel is a VHF band televisionsignal. The control signal BSV is generated by an integrated circuit 222here shown as an additional function of a phase locked loop (PLL) IC.The control signal BSV is a voltage generated by the PLL 222 in responseto a channel selection signal. This may be under control of theprocessor 50.

The tuner 40 has a UHF processing portion 204, a VHF processing portion206, a mixer/oscillator portion 214, the PLL 222, and a digital toanalog converter (DAC) 224 that may provide a voltage control generator(58) function. The UHF processing portion 204 is operative to tune aparticular UHF channel (particular television signal) in response tochannel selection. The VHF processing portion 206 is operative to tune aparticular VHF channel (particular television signal) within aparticular VHF band (here one of two VHF bands) in response to channelselection.

The UHF processing portion 204 includes a single tuned (ST) input filter208 as an adjustable or tunable input filter in accordance with thepresent principles that is connected to the U/V splitter 202 so as toreceive the output of the U/V splitter 202. Particularly, the UHFsignals are received by the tunable input filter 208 from the U/Vsplitter 202. The tunable input filter 208 operates over a particularvoltage range depending on design parameters, particularly a continuousanalog voltage. A control voltage signal, designated ST, is received bythe tunable input filter 208 that allows the frequency response of thetunable input filter 208 to be adjusted per the present principles. TheDAC 224 may use the LO tuning voltage to produce the control voltage forthe tunable input filter, with or without a stored offset signal (asemi-independent control voltage signal with regard to the localoscillator, LO) or the control voltage ST may be supplied to the tunableinput filter 208 by a voltage generator that is independent of the localoscillator (LO) in response to the channel selection signal. The voltagesignal ST allows the single tuned filter 208 to tune the selectedchannel and be adjustable in its frequency response.

The output of the tunable input filter 208 is provided to an RFamplifier (amp) 210. The RF amplifier 210 is operative to amplify the RFUHF signal from the tunable input filter 208 according to an RF AGC(automatic gain control) signal produced by the television signalreceiver. The RF amplifier 210 is also operative to receive a UHF bandselect signal (BSU) generated by and from the PLL 222. The UHF bandselect signal BSU is generated by the PLL in response to the channelselection signal. The band select signal BSU is essentially an on/offsignal for the RF amplifier 210.

The output of the RF amplifier 210 is provided to a double tuned (DT)filter 212. In this embodiment, the double tuned filter 210 operatesover a zero to five (0-5) volt range. It may be appreciated that othertechniques may be employed, e.g., variable reactance (e.g., voltagevariable reactance or varactor) filter techniques employing voltagessimilar to and derived more directly from the LO tuning voltage.Particularly, the double tuned filter 210 operates over a continuousanalog voltage from zero to five (0-5) volts. A zero to five voltsignal, designated PRI, is received from the DAC 224. The DAC 224produces the zero to five volt signal (i.e. the continuous analog 0-5volt signal) PRI in response to the channel selection signal. The PRIvoltage signal allows the first portion of the double tuned filter 212to tune the selected channel. A zero to five volt signal, designatedSEC, is also received from the DAC 224. The DAC 224 produces the zero tofive volt signal (i.e. the continuous analog 0-5 volt signal) SEC inresponse to the channel selection signal. The SEC voltage signal allowsthe second portion of the double tuned filter 212 to tune the selectedchannel.

The output of the double tuned filter 212 is provided to themixer/oscillator 214, shown in the form of an IC. It should beappreciated that the mixer portion and the oscillator portion may beseparate, but is shown combined. In particular, the output of the doubletuned filter 212 is provided to a mixer 228. A UHF local oscillator (LO)226 has an output connected to the mixer 228. The UHF LO 226 isoperative to receive a local oscillator (LO) tuning voltage signal fromthe PLL 222 and generate a tuned local oscillator signal. The LO tuningvoltage signal is produced by the PLL in response to the channelselection signal. The LO tuning voltage signal is an analog voltagesignal from zero to thirty (0-30) volts. The UHF LO 226 also providesfeedback to the PLL 222 in the form of an LO drive signal.

The UHF mixer 228 combines or mixes the tuned UHF local oscillatorsignal from the UHF LO 226 with the output signal (selected channel) ofthe double tuned filter 212. The output of the mixer 228 is provided toa double tuned intermediate frequency (IF) filter 234. The double tunedIF filter 234 provides its output to an IF amplifier (amp) 236. Theamplified IF signal (selected television channel) from the IF amplifier236 is then provided to the measurement circuitry/logic 56.

The VHF processing portion 206 includes a single tuned (ST) input filter216 as an adjustable or tunable filter in accordance with the presentprinciples that is connected to the U/V splitter 202 so as to receivethe output of the U/V splitter 202. Particularly, the VHF signals arereceived by the tunable input filter 216 from the U/V splitter 202. Thetunable input filter 216 operates over a particular voltage rangedepending on design parameters, particularly a continuous analogvoltage. A control voltage signal, designated ST, is received by thetunable input filter 216 that allows the frequency response of thetunable filter 216 to be adjusted per the present principles. The DAC224 may use the LO tuning voltage to produce the control voltage for thetunable input filter 216 with or without a stored offset signal orvoltage (a semi-independent control signal with regard to the LO) or thecontrol voltage (ST) supplied to the tunable input filter 216 may besupplied by a voltage generator that is independent of the LO inresponse to the channel selection signal. The voltage signal ST allowsthe single tuned filter 216 to tune the selected channel and beadjustable in its frequency response.

Additionally, the tunable input filter 216 is operative to receive aband select signal (BS 1/2) produced by and therefore from the PLL 222.The band select signal (BS 1/2) selects one of two VHF bands.Particularly, band select signal (BS 1/2) is an on/off voltage signalderived from the channel selection signal.

The output of the tunable input filter 216 is provided to an RFamplifier (amp) 218. The RF amplifier 218 is operative to amplify the RFVHF signal from the tunable input filter 216 according to an RF AGC(automatic gain control) signal produced by the television signalreceiver. The RF amplifier 218 is also operative to receive a VHF bandselect signal (BSV) generated by and from the PLL 222. The VHF bandselect signal BSV is generated by the PLL in response to the channelselection signal. The band select signal BSV is essentially an on/offsignal for the RF amplifier 218.

The output of the RF amplifier 218 is provided to a double tuned (DT)filter 220. The double tuned filter 220 operates over a zero to five(0-5) volt range. Particularly, the double tuned filter 220 operatesover a continuous analog voltage from zero to five (0-5) volts. A zeroto five volt signal, designated PRI, is received from the DAC 224. TheDAC 224 produces the zero to five volt signal (i.e. the continuousanalog 0-5 volt signal) PRI in response to the channel selection signal.The PRI voltage signal allows the first portion of the double tunedfilter 220 to tune the selected channel. A zero to five volt signal,designated SEC, is also received from the DAC 224. The DAC 224 producesthe zero to five volt signal (i.e. the continuous analog 0-5 voltsignal) SEC in response to the channel selection signal. The SEC voltagesignal allows the second portion of the double tuned filter 220 to tunethe selected channel.

Additionally, the double tuned filter 220 is operative to receive theband select signal (BS 1/2) produced by and therefore from the PLL 222.The band select signal (BS 1/2) selects one of two VHF bands.Particularly, band select signal (BS 1/2) is an on/off voltage signalderived from the channel selection signal. The band select signal (BS1/2) is the same as provided to the single tuned filter 216.

The output of the double tuned filter 220 is provided to themixer/oscillator 214, shown in the form of an IC. It should beappreciated that the mixer portion and the oscillator portion may beseparate, but is shown combined. In particular, the output of the doubletuned filter 220 is provided to a mixer 232. A VHF local oscillator (LO)230 has an output connected to the mixer 232. The VHF LO 230 isoperative to receive a local oscillator (LO) tuning voltage signal fromthe PLL 222 and generate a tuned local oscillator signal. The LO tuningvoltage signal is produced by the PLL in response to the channelselection signal. The LO tuning voltage signal is an analog voltagesignal from zero to thirty (0-30) volts. The VHF LO 230 also providesfeedback to the PLL 222 in the form of an LO drive signal.

The VHF mixer 232 combines or mixes the tuned VHF local oscillatorsignal from the VHF LO 230 with the output signal (selected channel) ofthe double tuned filter 220. The output of the mixer 232 is provided tothe double tuned intermediate frequency (IF) filter 234. The doubletuned IF filter 234 provides its output to the IF amplifier (amp) 236.The amplified IF signal (selected television channel) from the IFamplifier 236 is then provided to the measurement circuitry/logic 56.

The measurement circuitry/logic 56, in addition to other functions, isused to determine the tuning of the respective tunable input filter. Themeasurement circuitry/logic 56 includes a wide band detector 238 that isoperative to ascertain parameters (e.g. AGC, signal strength or thelike) of the television signal within a relatively wide a frequencyrange around the particular frequency of the television channel beingtuned. At this point, the received signal probably includes severaltelevision channels. This aids in determining whether the signal beingreceived is actually of the frequency of the television channel thatshould be tuned in response to the channel selection, or of a frequencyof an adjacent television channel being tuned. As discussed with respectto a manner of operation of the subject invention, the television 20ascertains all of the television channels that are being receivedthrough the antenna system 24.

Once wide band detection 238 has been accomplished, the televisionsignal is provided to an amplifier (amp) 240. Thereafter, the amplifiedtelevision signal is provided to a SAW filter 242. The SAW filter 242attempts to restrict the television signal to a single televisionchannel and reject the adjacent undesired signals. Thereafter, thetelevision signal is provided to a narrow band detector 244. The narrowband detector 244 is operative to ascertain parameters (e.g. AGC, signalstrength or the like) of the television signal within a relativelynarrow frequency range around the particular frequency of the televisionchannel being tuned. This aids in trying to determine whether thetunable input filter has been optimally tuned to receive the selectedtelevision channel. Thereafter, the television signal is provided tofurther processing.

The channel selection signal is typically, but not necessarily, producedby the television signal receiver having the electronic alignment systemin response to user input. The channel selection signal is provided tothe DAC 224 and the PLL 222. While other manners of providing thechannel selection signal are contemplated, the electronic alignmentsystem 200 is shown utilizing the I²C (or IIC) configuration/protocol.As such, an I²C clock line and an I²C data line is shown connected tothe DAC 224 and the PLL 222. Both the PLL 222 and the DAC 224 produce ananalog voltage signal continuously ranging from zero (0) to a maximumvoltage which, in the case of the DAC 224 is five (5) volts, and in thecase of the PLL 222, is thirty (30) volts.

Recapitulating, the television 20 includes an electronically tunableinput filter (e.g. 208, 216) as part of the tuner. The tunable inputfilter is tunable as to a passband frequency range via a control voltageapplied thereto. The frequency range and the center frequency of thefilter 60 is controlled by varying a control voltage applied thereto.The control voltage is produced in response to a performance measurementor measurements of received television signals as provided herein. Inaccordance with the principles of the subject invention, this providescompensation at the tuner 40 for the effects of the variations fromnominal of impedance 29 that was not considered in the design of thetuner 40.

In accordance with the principles of the subject invention, the tuner40, under control of the processor 50, is tunable to a particulartelevision channel or channels. The output of the tuner 40 is coupled tomeasurement circuitry/logic 56. The measurement circuitry/logic 56 isoperative, configured and/or adapted to obtain performance measurements(metrics) of the tuned television channel or channels in order todetermine whether frequency response adjustment of the tunable inputfilter in the form of a center frequency adjustment or frequency band orrange (bandpass range) needs to be made to the tunable input filter. Themeasurement circuitry/logic 56 may look at RF AGC (automatic gaincontrol) metrics, signal quality, or otherwise, depending on whether thetelevision signal is analog or digital, as well as other considerations.The measurement(s) are provided to the processor 50 for analysis.

The processor 50 is controlled by the program instructions 52 stored ina memory such as ROM, in order to provide the functionality describedherein. The processor 50 obtains signal measurements and determineswhether an improvement in signal quality is desired. If it is determinedthat no improvement in signal quality is necessary, control voltage datapreviously stored in a memory 54 is used to allow the control voltagegenerator 58 to provide the desired control voltage to the tunable inputfilter. This control voltage data is the “nominal” data for the tuner 62as designed for the 75 ohms CATV input (or other “designed for” signalinput system).

If it is determined that an improvement in signal quality is necessary,the processor 50 causes the control voltage generator 58 to adjust thecontrol voltage supplied to the tunable input filter. This changes thefilter frequency range thereof and/or the center frequency thereof.Thereafter, new measurement(s) taken. The adjustment in control voltageis preferably made to provide an increment in center frequency of thetunable filter 60 and a decrement in center frequency or frequency rangeof the tunable input filter (each with respect to the nominal frequencywith respect to a 75 ohm CATV input), after which, each time ameasurement or measurements are taken. The more optimum control voltageis retained. This process is repeated until a suitable signal quality isobtained, the control is at a preset limit or no further improvement canbe obtained.

Once the adjustment is complete, this new control voltage value isstored in the memory 54. The program instructions also allow forre-adjustment for various reasons. It should be appreciated that theblocks depicted in the figures and described above are not necessarilyseparate components, circuitry or the like, but represent functionalityof the television 20. Some blocks may represent actual components of thetelevision.

Referring now to FIG. 4, there is depicted a flowchart, generallydesignated 60, of an exemplary manner of providing compensation forimpedance at the input to an RF tuner, and particularly the electronicadjustment of the frequency response of an electronically adjustable RFinput filter, in accordance with the principles of the subjectinvention. It should initially be appreciated that while the methoddescribed is in connection with a tuner in a television signal receiver(e.g. a television), the subject invention may be utilized by othertypes of RF signal receivers. The compensation may be adjustment of thecenter frequency of the tunable input filter or the adjustment of thebandpass frequency range of the tunable input filter.

In block (step) 62 the antenna television signal input is selected.Thereafter, in block 64 a particular television channel is selected. Thetelevision, in block 66, then tunes to the selected television channel.After the selected television channel is tuned, in block 68, a parameterof the tuned television channel is measured. In block 70, from themeasured parameter of the tuned television channel, signal quality ofthe tuned television channel is determined.

In block 72, the frequency response of the tunable input filter isadjusted. Thereafter, in block 74, the measuring, determining andadjusting is repeated until an optimal signal quality for the televisionchannel being tuned is reached. Adjustment of the tunable input filtermay be such that a frequency response thereof has a center frequencythat corresponds to the frequency of the television channel being tunedas shifted by the impedance of the antenna, as compared to the normalfrequency for the particular television channel. Adjustment of thetunable input filter may be such that a frequency response thereof has apassband frequency range that includes the frequency of the televisionchannel being tuned as shifted by the impedance of the antenna, ascompared to the normal frequency for the particular television channel.

Referring now to FIG. 5, there is depicted an exemplary tunable inputfilter generally designated 100 that may be used as the single tunedfilter 208 or 216 of the electronic alignment tuner 40 of FIG. 3. Thetunable input filter 100 allows for an input transformer 110 thereof tobe variable. The tunable input filter 100 has a first varactor diode 102that is provided in a shunt configuration with the antenna input (“FromAntenna”) and the output of the filter (through the varactor diode 106and amplifier (field effect transistor) 108). The amplifier 108 providesthe AGC and has its output connected to the radio frequency (RF) doubletuned (DT) filter. A second varactor diode 104 is provided in serieswith the antenna and the output of the filter. Various capacitors andresistors are provided as necessary. This configuration allows for theadjustment of the transform ratio thereof. The same control voltage(Tuning Voltage 1) is provided to the varactor diodes 102 and 104. Thecontrol voltage is thus common to both varactors but is still preferablyindependent of the local oscillator voltage.

In FIG. 6, the tunable input filter 100 is shown having the same circuitelements and arrangement as the tunable input filter 100 of FIG. 5. Inthe tunable filter 100 of FIG. 6, however, separate control voltages areapplied to each varactor. Particularly, the tuning voltage 1 as thecontrol voltage is provided to the series varactor 104, while a tuningvoltage 2 as a separate control voltage is applied to the shunt varactor102. This case allows for the continuously variable adjustment of thecapacitance of each varactor base on the control voltage which, in turn,allows for the adjustment of both the transform ratio and tuningfrequency of the filter.

It should be appreciated that the capacitance values of the varactorsshould be appropriately chosen for proper operation. One criteria isthat the capacitance values be different from one another. Moreover, inorder to allow for a significant adjustment range, each diode mustpossess some excess adjustment range over the nominal operating range.

The above exemplary tunable input filters are operative to provideperformance improvement in tuning of the tuner in which they are a part,through adjustment thereof, particularly when off-air reception(antenna) is selected. Particularly, the filters of FIGS. 5 and 6provide adjustable frequency ranges (frequency response) to compensatefor shifts or “mistuning” as a result of off-air antenna impedance onthe tuner.

Referring now to FIG. 7, there is depicted an exemplary tunable inputfilter generally designated 100 a that may be used as the single tunedfilter 208 or 216 of the electronic alignment tuner 40 of FIG. 3. Theconfiguration of the filter 100 a is identical to the configuration ofthe filter 100 of FIG. 5, with the exception of a boost control voltagescaling circuit 112. The boost control voltage scaling circuit 112 isprovided between the tuning voltage 1 and the shunt varactor diode 102a. A boost control signal input is provided to the boost control voltagescaling circuit 112 that provides a boost control signal if desired.

If the boost control voltage scaling circuit 112 is activated by theboost control signal, the shunt control voltage (tuning voltage 1) ispassed through the boost voltage scaling circuit 112 that scales(fixedly increments) the voltage downward. The capacitance of thevaractor 102 a is now larger and allows for a reduction in the transformratio, increasing the loaded Q and decreasing the bandwidth. The typicalformula for this bandwidth relates the ratio of the two capacitors as abandwidth. Bandwidth is proportional to the sum of (C102 and C104)squared divided by C104 squared. In this case, the filter 100 a providesa known bandwidth increase, not an adjustable one as with the filter 100of FIG. 5.

In FIG. 8, the filter 100 a uses two control voltages, tuning voltage 1and tuning voltage 2 in like manner to the filter of FIG. 6. In thisconfiguration, the switched bandwidth is larger than the bandwidth ofthe filter of FIG. 7.

While the above filters of FIGS. 5-8 may not be used with tuners havingelectronic alignment, the use of such filters in tuners with electronicalignment or adjustment can now change the control voltage to one orboth diodes (depending on which filter is used) to re-center thefrequency response (or change the bandwidth and collectively, change thefrequency response thereof) with the effectively wider bandwidth. Again,the capacitance values of the diodes must be appropriate for properoperation, but need to be different from each other. In order to allowfor a significant adjustment range, each diode must possess some excessadjustment range over the nominal operating range.

Referring now to FIG. 9, there is depicted a flowchart, generallydesignated 150, of another exemplary manner of providing compensationfor impedance at the input to an RF tuner, and particularly theelectronic adjustment of the frequency response of an electronicallyadjustable RF input filter, in accordance with the principles of thesubject invention. Such frequency response adjustment may be to thecenter frequency with respect to the television channel being tuned, orwith respect to a bandwidth encompassing the television channel beingtuned. It should initially be appreciated that while the methoddescribed is in connection with a tuner in a television signal receiver(e.g. a television), the subject invention may be utilized by othertypes of RF signal receivers.

In block (step) 152, the television is turned on and an auto-searchroutine is initiated. Because a television is typically connected toonly one of an antenna and a cable system, but not both at the sametime, the auto-search routine is typically only performed during aninitial set-up of the television. However, in the event that thetelevision becomes unconnected to a source of electricity for a periodof time (or the electricity is off), the auto-search routine may beinitiated again. Once the auto-search routine is initiated, theauto-search routine then assesses, in block 154, whether the televisionis receiving television channels (signals) via a cable television (CATV)system (i.e. cable) or over the air (i.e. air) via an antenna. Whilesuch an assessment may be accomplished in various manners, one suchmanner is to pick a television signal (antenna or cable) input, attemptto tune to one or more particular television channels, and determinewhether valid television signals are present. If the chosen televisionsignal input does not yield any valid television signals, the othertelevision signal input is chosen, with the search and determinationscheme renewed. As an alternative routine, the television may prompt theuser to select whether a CATV system is being used or an antenna as thesource of television signals.

If the television (or user, as the case may be) determines that cable isbeing used as the television signal input, the factory default settings(e.g. control voltage) for the subject electronically adjustable RFfilter are used, block 156. As indicated above, the settings for theelectronically adjustable RF filter are based on the good 75 ohm CATVcabling system. If the television (or user, as the case may be)determines that an antenna (air) is being used as the television signalinput, the method 150 moves to block 158.

In block 158, the located television channels are recorded or stored ina channel list. Additionally, an approximate signal level (depending onwhether the television signals are analog, NTSC, or digital, ATSC) basedon a signal level parameter such as AGC settings, and/or signal quality,for each television channel is stored. Then in block 160, a televisionchannel is tuned in the air (antenna) mode. The television channelchosen is according to selection typically by the user. In block 162,the signal level of the television channel as tuned is assessed. Suchassessment is by measuring a parameter of the signal. A parameter of thesignal may be its corresponding AGC value in the case of an analogsignal, and signal quality in the case of a digital signal. This value(or these values) is/are stored for reference. Additionally, accordingto the channel list, the proximity of television channels adjacent theselected and tuned television channel are identified. The parametervalues of these are also stored or imaged.

When the user selects a desired channel, the information for the desiredchannel is first retrieved, including the information regarding itsassessment of signal parameters as indicated above. The processor in thetelevision also looks to determine if additional signals near thedesired signal are available. The method for this may involve a numberof key parameters that may depend on the design of the tuner forinstance, but one method may involve looking only for adjacent or secondadjacent channels present. In any case, these assessments are then usedin order to provide an aid to the “tuning” of the input filter byproviding some indication of an error occurrence in the algorithm. In aparticular instance, the “retuning” may begin to center the input filteron the adjacent channel and depending on various signal levels mayprovide a reading of desired signal assessment that is in error due tothe presence of the adjacent channel. In this way the storage of signalassessments for each signal received can aid in the improvement of thedesired signal tuning.

In block 164, the subject input filter is then adjusted for a bettersignal. This is accomplished by changing the voltage control signal tothe filter and/or by providing a boost control signal. Such voltagecontrol signal adjusts the frequency response of the input filter. Achange in frequency response affects the center frequency of passbandfrequencies and/or a passband frequency range upwards or downwards asthe case may be. Thereafter, in block 166, the narrow band AGC (NBAGC),the wide band AGC (WBAGC) and/or the signal quality (signal parametervalues) are measured again with respect to the tuned television channeland assessed or compared to the previously stored values (signalparameter values).

The analysis of the narrow band and the wide band parameter values arepreferably necessary in order to make sure that the energy of adjacentchannels are not falsely perceived as coming from the channel beingtuned. The narrow band and wide band values are thus analyzed withrespect to the knowledge of which television channels are available andadjacent to the television channel being tuned.

As indicated in block 168, the adjustment process is repeated in boththe upwards and downwards positions until the signal parameter valuesindicates an optimal condition for the tuned channel is achieved oradjustment range conditions are met. Thereafter, the new filter settingsare stored. In one embodiment, a DAC (digital to analog converter) isutilized to provide the control voltage to the subject input filter andan EEPROM is used to store the settings. Each channel may have its ownvoltage value.

If the control voltage signal is semi-independent of the localoscillator, the voltage control value may be stored as an offset to thenominal voltage control value and applied as necessary. If the controlvoltage signal is independent of the local oscillator, the voltage valueis stored and provided to the control voltage generator as appropriate.

The subject invention expands the capability of an RF receiver,particularly one using at least one electronically adjustable RF filterat the input of a tuner, by allowing the receiver to adjust the inputfilter center frequency in response to the presence of unexpectedimpedance present at the antenna input. In one form, the subjectinvention utilizes an algorithm for determining the necessaryadjustment, with the algorithm getting its inputs from a source such asthe AGC system, a digital signal level meter downstream in the receiver,or the like depending, in part, on whether the RF signal is analog ordigital. Adjustment may be in the form of frequency responsemodification, such as adjustment of the center frequency and/or passbandfrequency range.

As a recapitulation, the subject invention takes advantage of theability to adjust the RF input filter dynamically in the field based onthe actual input impedance presented by the antenna and cable used. Thesubject RF input filter is nominally designed for operation at 75 ohmsinput. This is the default setting and it is also the setting to use forcable (CATV) reception. However, if off-air reception (antenna) isselected as the RF signal input, a performance improvement may bepossible through adjustment of the input filter based on the antennaused. In this case, the tuner is still set for nominal conditions whenfirst tuned. The performance measurements on RF AGC are determined aswell as determining signal quality. If the indication from thesemeasurements show that an improvement may be desirable, then the inputfilter control voltage is adjusted in each direction away from nominal(up or down in frequency) and the improvement monitored. Once theadjustment is complete, the new control voltage value can be stored in aseparate memory location to be retrieved for future channel selections.Provisions will also allow for re-adjustment in the case where adifferent antenna or configuration becomes employed.

It has been determined through testing, that the adjustment range doesnot have to be very large and can also be artificially restricted toprevent a “trapping” condition. The monitoring system includes thedetermination of signal environment to detect the presence of adjacentchannels in order to keep from optimizing on the wrong signal.Additionally, while using the AGC value has been indicated herein as thepreferred detection method for movement, it should be appreciated thatother metrics such as signal quality (digital signals), pix to soundratio, and the like may be utilized.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, of adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. A method of tuning a signal channel comprising: (a) selecting asignal channel to be tuned; (b) tuning the selected signal channel byapplying a filter control signal to an electronically tunable inputfilter of a signal tuner, the filter control signal causing a passbandfrequency bandwidth of the electronically tunable input filter toencompass an expected frequency of the signal channel to be tuned; (c)monitoring a performance measurement of the tuned signal channel; (d)generating a first control signal based on monitored performancemeasurement; (e) retuning the selected signal channel by applying thefirst control signal to the electronically tunable input filter, thefirst control signal adjusting the passband frequency bandwidth of theelectronically tunable input filter, wherein the first control signal isapplied to a first variable reactance shunted with respect to an inputand an output of the electronically tunable input filter, and to asecond variable reactance in series with the input and the output, andwherein the first and second variable reactances comprise respectivefirst and second varactors and wherein the first control signalcomprises a first control voltage that is applied to the first varactorthrough a voltage scaling circuit that is operative to provide a fixedincrease in the passband frequency bandwidth of the electronicallytunable input filter upon receipt of a scaling signal; and (f) repeatingsteps (c), (d) and (e) until the adjusted passband frequency bandwidthof the electronically tunable input filter encompasses the frequency ofthe selected signal channel as received at an approximate centerfrequency of the adjusted passband frequency bandwidth.
 2. The method ofclaim 1, further comprising: applying the scaling signal to the voltagescaling circuit to increase the passband frequency bandwidth of theadjusted passband frequency bandwidth.
 3. The method of claim 1, whereinretuning the selected signal channel includes applying a second controlsignal to the electronically tunable input filter, the second controlsignal adjusting the passband frequency bandwidth of the electronicallytunable input filter in conjunction with the first control signal. 4.The method of claim 1, wherein monitoring the performance measurement ofthe tuned signal channel includes measuring a parameter of the tunedsignal channel.
 5. The method of claim 4, wherein the tuned signalchannel comprises a tuned television channel and wherein measuring theparameter of the tuned signal channel includes measuring AGC in the caseof an analog television channel else measuring signal quality and/or AGCin the case of a digital television channel.
 6. The method of claim 5,wherein measuring AGC includes measuring a narrow band AGC principallyresponsive to a desired channel and a wide band AGC and responsive toboth the desired channel and adjacent undesired signals.
 7. The methodof claim 1, further comprising: obtaining information of potentialinterfering channels from a programmed search of available channels; andusing the obtained information of potential interfering channels toadjust the first control signal for optimum reception.
 8. A system fortuning a television channel comprising: a processor operative to executeprogram instructions; a television channel tuner coupled to saidprocessor and having an electronically adjustable input filter; acontrol voltage generator coupled to said processor and saidelectronically adjustable input filter; measuring circuitry/logiccoupled to said processor and an output of said television channeltuner; and memory coupled to said processor and containing a pluralityof program instructions, said processor operative to cause, thetelevision channel tuning system to: (a) select a television channel tobe tuned; (b) tune the selected television channel by applying a filtercontrol voltage to the electronically tunable input filter of thetelevision signal tuner, the filter control voltage causing a passbandfrequency bandwidth of the electronically tunable input filter toencompass an expected frequency of the television channel to be tuned;(c) monitor a performance measurement of the tuned television channel;(d) generate a first control voltage based on monitored performancemeasurement; (e) retune the selected television channel by applying thefirst control voltage to the electronically tunable input filter, thefirst control voltage adjusting the passband frequency bandwidth of theelectronically tunable input filter, wherein the first control voltageis applied to a first varactor shunted with respect to an input and anoutput of the electronically tunable input filter, and to a secondvaractor in series with the input and the output, and wherein the firstcontrol voltage is applied to the first varactor through a voltagescaling circuit that is operative to provide a fixed increase in thepassband frequency bandwidth of the electronically tunable input filterupon receipt of a scaling signal; and (f) repeat (c), (d) and (e) untilthe adjusted passband frequency bandwidth of the electronically tunableinput filter encompasses the frequency of the selected televisionchannel as received at an approximate center frequency of the adjustedpassband frequency bandwidth.
 9. The system of claim 8, wherein thesystem has further program instructions wherein said processor operatesto cause, the system to further to: apply the scaling signal to thevoltage scaling circuit to increase the passband frequency bandwidth ofthe adjusted passband frequency bandwidth.
 10. The system of claim 8,wherein retune the selected television channel includes applying asecond control voltage signal to the electronically tunable inputfilter, the second control voltage adjusting the passband frequencybandwidth of the electronically tunable input filter in conjunction withthe first control voltage.
 11. The system of claim 8, wherein monitoringthe performance measurement of the tuned television channel includesmeasuring a parameter of the tuned television channel.
 12. The system ofclaim 11, wherein measuring the parameter of the tuned televisionchannel includes measuring AGC in the case of an analog television elsemeasuring signal quality and/or AGC in the case of a digital televisionchannel.
 13. The system of claim 12, wherein measuring AGC includesmeasuring a narrow band AGC principally responsive to a desired channeland a wide band AGC and responsive to both the desired channel andadjacent undesired signals.
 14. The system of claim 8, wherein thesystem has further program instructions, wherein said processor operatesto causes the system further to: obtain information of potentialinterfering channels from a programmed search of available channels; anduse the obtained information of potential interfering channels to adjustthe first control voltage for optimum reception.